[time-nuts] Input filter for data logger

[Vlad]

Hello,

I am doing another fun project. It is data logger at this time. The 
"heart" is MV89A OCXO and the "brain" is STM32.
"The box" has 1PPS input to control DAC which will control OCXO. BTW, 
this M89A is pretty hot to touch. My other OCXO's not that much warmed. 
Is it normal for this Morion model ?
I woul ask an advise regarding following issue. I have signal generator 
which produce the square wave. The freq. is 192Hz.

http://www.patoka.org/OCXO/LOGGER/IMG_20171119_104659813.jpg

However, the logger measure it TWICE ! I think its because of that 
signal form. Here is the output (in microseconds):

http://www.patoka.org/OCXO/LOGGER/IMG_20171119_104838190.jpg

In average delta is .0026041 s, which is almost equal to 384 Hz (192x2)

For the input I am using the schema similar as HP was using in one of 
their counters:

http://www.patoka.org/OCXO/LOGGER/IMG_20171110_123201987.jpg


I tried another source (DDS sine generator, referenced from GPSDO) and 
that beast produce exact number of events:

26.5404621
26.5473008
26.5525067
26.5577297
26.5629260
26.5681280
26.5733305
26.5785262
26.5837255
26.23559295
26.5941842
26.5993546
26.6045699
26.6097716
26.6149911
26.6202076
26.6254149
26.6306244
26.6358103
26.6410386
26.6462491


However, it is some "spikes" in the data flow (see above the number 
"26.23559295", which suppose to be something as "26.58..."). I can't 
understand the reason for that.
The "delta" is .0052 s, which is almost equal to 192 Hz. But data flow 
is not that "smooth" though.

In square wave mode, "school grade" Wavetek generator produced exact 192 
events with no issues. (Except its output frequency is not that stable)

21.0578286
21.0630547
21.0682807
21.0735070
21.0787330
21.0839591
21.0891852
21.0944112
21.0996372
21.1048632
21.1100892

However, if I switch Wavetek to sine, my logger detected twice number of 
event (384)

97.0185559
97.0214570
97.0237852
97.0266822
97.0290048
97.0319054
97.0342336
97.0371408
97.0394552
97.0423578
97.0446802
97.0475836
97.0499131
97.0527969
97.0551313
97.0580259
97.0603560
97.0632648
97.0655869

I would assume, some improvement needs to be done for the data logger 
input. I am using 2N5485 and 74AC04 elements there. Any advises will be 
appreciated ! Thanks !


-- 
WBW,

V.P.